The refinery failed to prevent the unauthorized release 30,405.55 pounds of volatile organic compounds and 33.96 pounds of sulfur dioxide from a vapor line that started Oct. 12, 2012, and lasted 190 hours - two hours shy of eight days - agency records show.

Corrosion on an inlet nozzle on a caustic scrubber was responsible for the leak, agency records show.

ExxonMobil replaced the nozzle and modified the equipment as of Feb. 17, 2013, to mitigate future leaks to prevent recurrence of the emissions, agency records show.

The fine was evenly split with payments of $43,700 made to the state's general revenue fund and a supplemental environmental project, the Southeast Texas Regional Planning Commission's regional air monitoring network, agency records show.

The chemical plant released 14 pounds of hydrogen cyanide in 16 minutes on Oct. 10, 2012, when a valve became locked in a partially open position during a maintenance turnaround, agency records show.

The plant released 20 pounds of hydrogen cyanide and 350 pounds of carbon monoxide in four hours, eight minutes on Dec. 1, 2012, when plant operators failed to maintain required nitrogen pressure as a unit in the plant was restarted, agency records show.